In my experience, a 50% VF is associated with a wire lying on the ground and is in the lower end of measured VF's for wires laying on the ground. 45% is the lowest I have seen personally. A regular beverage up six to eight feet above ground will usually be 95% or better.
A BOG cut to certain lengths certainly WILL reverse pattern. Regular beverages will lose a good degree of front-to-back with unfortunate lengths which might render it useless with a given source of noise. Beverages closely parallel to long conductors, or with a blown termination/transformer, or dysfunctional grounding at either end can also develop unpredictable patterns. Slinky's have their own private discipline :>) 73, Guy K2AV On Mon, Jul 28, 2014 at 1:54 PM, Carl <[email protected]> wrote: > There is really nothing new to explain. It has been established since the > mid 1920's that the Beverage is a slow wave antenna, ie: it has a velocity > factor, and at an electrical 50% VF it will reverse direction. > > It doesnt take much effort or math to compute the electrical length > shortening of a Slinky and I believe I stated that mine was around 60% on > this reflector in the late 90's and I was supplying Slinkys to others in the > US and international. This was also picked up by ON4UN who published the > Slinky Beverage in one of the earlier revisions of his book with incomplete > data to easily reproduce. > > Using a 1590 BC station directly to the rear I determined the proper > termination resistance to be 1200 Ohms for the final version. This was > around 1987-88 and years before I even knew about any reflectors and > discussions were only on 160 SSB just above the DX window when the band was > dead. K1ZM gets the credit for planting the idea during one of those chats > and it didnt take me long to work out the details. Those 1987-88 experiments > took many forms and the number of Slinkys used and running 100-300'. Other > lengths required different terminations and transformers. After a certain > person started in with belittling comments I stopped posting and just shared > later data via direct emails or phone calls. > > Doing a Google on "KM1H Slinky Beverage" will give loads of hits and also > refreshed my memory...disregard the 18 month useful life...that was after > they were no longer cadmium plated. > > Carl > KM1H > > > > ----- Original Message ----- From: "Mike Waters" <[email protected]> > To: "topband" <[email protected]> > Sent: Monday, July 28, 2014 12:42 PM > > Subject: Re: Topband: Length of Beverages > > >> Hi Jim, >> >> As we move the turns closer, we increase the velocity factor too much. At >> some point, the Slinky will receive off the opposite (feed) end. Tom >> explains it at >> www.w8ji.com/slinky_and_loaded_beverages.htm . >> >> And I just found this, where K5UO seems to say that his Slinky was about >> 12 >> turns per foot. >> lists.contesting.com/_towertalk/2006-12/msg00510.html >> >> 73, Mike >> www.w0btu.com >> >> >> >> Mike, what do you mean when you say "fires backwards". >>> >>> >>> >>> >>> On 7/28/2014 8:59 AM, Mike Waters wrote: >>> >>>> Carl, >>>> >>>> On Sun, Jul 27, 2014 at 6:53 PM, Carl <[email protected]> wrote: >>>> >>>> I knew that answer 20 years ago Mike. Perhaps someone has a large >>>> Slinky, >>>>> >>>>> can count the turns and then give it back to his grandson (-: >>>>> >>>>> Ok. I think the thing to do is just experiment with the length/pitch. >>>> >>>> Stretch it out along the rope, past the point where it fires backwards >>>> (and >>>> then some), maybe. >>>> >>> ... >> >> _________________ >> Topband Reflector Archives - http://www.contesting.com/_topband >> >> >> ----- >> No virus found in this message. >> Checked by AVG - www.avg.com >> Version: 2014.0.4716 / Virus Database: 3986/7936 - Release Date: 07/28/14 >> > > _________________ > Topband Reflector Archives - http://www.contesting.com/_topband _________________ Topband Reflector Archives - http://www.contesting.com/_topband
